At present, the Chinese mobile service providers, such as China Mobile Communications Corporation and China United Telecommunications Corporation, have established domestic mobile intelligent networks in which value-added services can be provided and some prepaid services have been provided already. At the same time, mobile service providers in each area also have established local mobile intelligent networks in order to provide some value-added services that are suitable for this zone. During this process, billing for intelligent network subscribers in the province is implemented on intelligent platform. The overlay solution scheme is used in the process of establishing mobile intelligent networks. In this way, only a part of MSCs have the capability of SSP, and the MSCs without the capability of SSP forward the calls from the intelligent network subscribers to those with the capability of SSP in which corresponding service logic will be triggered and implemented. Therefore, any call that has been connected without passing an intelligent platform for billing will not be billed again. Thus, it is necessary for each call relating to intelligent network subscribers to be triggered to the intelligent platform.
For the local MSCs, through formulating data for calls, all calls relating to intelligent network subscribers can be directly forwarded to SSP in which corresponding service logic will be triggered to the intelligent platform. Nevertheless, in the case that a fixed phone subscriber or a non-local mobile phone subscriber calls a local intelligent network subscriber, since a Gateway Mobile Switching Center (GMSC) of another zone doesn't formulate data for the calls, the calls relating to the intelligent network subscribers cannot be routed to the local SSPs from the non-local GMSCs. In general, a GMSC directly obtains the roaming number of intelligent network subscribers from the Home Location Register (HLR) in which the intelligent network subscriber registered and directly routes the calls to the Visited Mobile Switching Center (VMSC) in which the intelligent network subscribers located without passing the intelligent platform of this zone for billing.